1. Field of the Invention
The invention relates to a process for synthesizing tertiary phosphines by reacting halophosphines with organomagnesium compounds in the presence of copper compounds and optionally of salts.
2. Brief Description of the Prior Art
Tertiary phosphines, and methods of using and preparing the same are generally known in the art. Many tertiary phosphines have a high industrial significance, for example as ligands for metal atoms for forming metal complexes, as reducing agents or, in the form of their oxides, as flame retardants or extractants. Metal complexes with tertiary phosphines are frequently used as catalysts in chemical reactions. Tertiary phosphines may also be used for absorbing metals, for example from liquid media.
Tertiary phosphines may typically be synthesized by reacting organometallic compounds with halophosphines. The organometallic compounds used are predominantly organomagnesium and organolithium compounds. However, with increasing steric demands of the organic radicals to be introduced or already present in the molecule, it becomes very difficult to obtain tertiary phosphines.
For example, phosphorus trichloride reacts with an excess of tert-butylmagnesium chloride to only give di(tert-butyl)chlorophosphine (see Hoffmann, Schellenbeck, Chemische Berichte, 1967, 100 (2), 692-693), or dichlorophenylphosphine reacts with an excess of tert-butylmagnesium chloride to only give tert-butylchlorophenylphosphine (see Hoffmann, Schellenbeck, Chemische Berichte, 1966, 99, 1134-1142).
In the synthesis of tricyclohexylphosphine from phosphorus trichloride and cyclo-hexylmagnesium compounds, the desired product is obtained only at high temperature and in low yields (see Issleib, Brack; Zeitschr. allg. anorg. Chem. 1954, 277, 258-270).
Stambuli et al. were able to demonstrate that when copper(I) iodide is added in the presence of lithium bromide, it is also possible to use organomagnesium compounds to obtain substitutions on bulky arylalkylchlorophosphines and tert-butylchlorophosphine (J. Am. Chem. Soc., 2001, 123 (11), 2677-2678). The high copper and salt requirements, and likewise the required reaction temperatures of −78° C., make the process industrially impracticable.
Kaye et al. (Adv. Synth. Catal., 2001, 343 (8), 789-794) describes the reaction of bis(aryl Grignard) compounds with chlorophosphines in the presence of copper(I) chloride, requiring large amounts of copper compounds, which complicates the industrial realization.
There was therefore the need to provide a process which makes it possible to synthesize tertiary phosphines in an efficient and industrially acceptable manner.